Engineering news
Silica aerogels are light, porous foams that provide excellent thermal insulation, but they are known for their brittle behaviour and are usually reinforced with fibres or biopolymers for large-scale applications. Due to their brittle fracture behaviour, it is also not possible to saw or mill small pieces out of a larger aerogel block. Directly solidifying the gel in miniaturised moulds is also not reliable, resulting in high scrap rates.
“This is why aerogels have hardly been usable for small-scale applications,” the announcement of the new research said. A team at the Swiss Federal Laboratories for Material Science and Technology (Empa) turned to 3D printing instead.
Led by Shanyu Zhao, Gilberto Siqueira, Wim Malfait and Matthias Koebel, the team succeeded in producing stable, well-shaped microstructures. The printed structures can reportedly be as thin as a tenth of a millimetre. The thermal conductivity of the silica aerogel is just under 16 mW/(m*K) – only half of polystyrene and significantly less than a non-moving layer of air (26 mW/(m*K)).
The printed silica aerogel reportedly also has better mechanical properties and can even be drilled and milled, opening up new possibilities for post-processing.
A patent application has been filed for the method, which makes it possible to adjust the flow and solidification properties of the silica ink, so that self-supporting structures and wafer-thin membranes can be printed. As an example of overhanging structures, the researchers printed leaves and blossoms of a lotus flower. The test object floats on water due to the hydrophobic properties and low density of the silica aerogel. The new technology also makes it possible to print complex 3D multi-material microstructures.
“With such structures it is now comparatively trivial to thermally insulate even the smallest electronic components from each other,” the research announcement said. “The researchers were able to demonstrate the thermal shielding of a temperature-sensitive component and the thermal management of a local ‘hot spot’ in an impressive way.”
Another potential application is the shielding of heat sources inside medical implants, which should not exceed a surface temperature of 37ºC to protect body tissue.
The researchers also constructed a ‘thermos-molecular gas pump’. The permeation pump, also known as a Knudsen pump, is based on the restricted gas transport in a network of one-dimensional channels. One end of the channels has hot walls, while the other end is cold. The team built such a pump from aerogel, which was doped on one side with black manganese oxide nanoparticles. When placed under a light source, it becomes warm on the dark side and starts to pump gases or solvent vapours.
If the air is contaminated with a pollutant or an environmental toxin such as the solvent toluene, the air can circulate through the membrane several times and the pollutant is chemically broken down by a reaction catalysed by the manganese oxide nanoparticles. Such a simple and durable solar-powered pump could be very appealing for air analysis and purification.
The Empa researchers are looking for industrial partners who want to integrate 3D-printed aerogel structures into new high-tech applications.
The research was published in Nature.
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